Asymmetric synthesis of 2,3-epoxyamides by reacting monosaccharide derivatives with stabilised sulphur ylides generated in-situ: two-phase method and configurational assignations
“…Dihydroxylation of the olefin37 and subsequent oxidative cleavage of the resulting diol with NaIO 4 38 afforded the required aldehyde 49 in 89 % yield. This aldehyde was then subjected to a second sulfonium ylide reaction by treatment with 1 in the presence of base using a two‐phase protocol to avoid possible epimerization side‐reactions 39. Epoxy amide 50 was obtained in 73 % yield and with excellent stereoselectivity.…”
The hydrotris(pyrazol‐1‐yl)methane iron(II) complex [FeCl2{η3‐HC(pz)3}] (pz=pyrazol‐1‐yl) (1) was immobilized on three different carbon materials (activated carbon, carbon xerogel and multi‐walled carbon nanotubes) with three different surface treatments (original, treated with nitric acid, and treated with nitric acid followed by sodium hydroxide) to produce active, selective and recyclable catalysts. The heterogenisation process was more efficient for carbon nanotubes treated with nitric acid and sodium hydroxide. An outstanding improved catalytic performance of complex 1 upon heterogenisation on carbon nanotubes treated with nitric acid and sodium hydroxide (turnover numbers up to 5.6×103 and overall yield of 21 %), relative to the homogeneous system, was achieved for the single‐pot peroxidative oxidation of cyclohexane to the cyclohexanone and cyclohexanol mixture. The heterogenised systems allowed their easy recovery and reuse, at least for five consecutive cycles, maintaining 96 % of the initial activity and concomitant rather high selectivity to cyclohexanol and cyclohexanone.
“…Dihydroxylation of the olefin37 and subsequent oxidative cleavage of the resulting diol with NaIO 4 38 afforded the required aldehyde 49 in 89 % yield. This aldehyde was then subjected to a second sulfonium ylide reaction by treatment with 1 in the presence of base using a two‐phase protocol to avoid possible epimerization side‐reactions 39. Epoxy amide 50 was obtained in 73 % yield and with excellent stereoselectivity.…”
The hydrotris(pyrazol‐1‐yl)methane iron(II) complex [FeCl2{η3‐HC(pz)3}] (pz=pyrazol‐1‐yl) (1) was immobilized on three different carbon materials (activated carbon, carbon xerogel and multi‐walled carbon nanotubes) with three different surface treatments (original, treated with nitric acid, and treated with nitric acid followed by sodium hydroxide) to produce active, selective and recyclable catalysts. The heterogenisation process was more efficient for carbon nanotubes treated with nitric acid and sodium hydroxide. An outstanding improved catalytic performance of complex 1 upon heterogenisation on carbon nanotubes treated with nitric acid and sodium hydroxide (turnover numbers up to 5.6×103 and overall yield of 21 %), relative to the homogeneous system, was achieved for the single‐pot peroxidative oxidation of cyclohexane to the cyclohexanone and cyclohexanol mixture. The heterogenised systems allowed their easy recovery and reuse, at least for five consecutive cycles, maintaining 96 % of the initial activity and concomitant rather high selectivity to cyclohexanol and cyclohexanone.
“…The epoxidation of 2,3- O -isopropylidene- d -glyceraldehyde 93a and its homologues 93b and 93c with dimethylsulfonium methylide and dimethylsulfoxonium methylide was reported by Anthonsen and co-workers (Scheme ). , Diastereoisomerical epoxides 94 and 95 were obtained in moderate yields and de values. Much higher diastereocontrol has been achieved in the reaction of the stabilized sulfonium ylide 96 and aldehyde 93a and other monosaccharide derivatives (Scheme ). ,63a 2,3-Epoxy amides with up to 92% de in favor of the anti adduct 97 was obtained. However, such high diastereoselectivity was not seen in reactions of other aldoses and ketoses.…”
Section: Other Related Reagentsmentioning
confidence: 99%
“…However, such high diastereoselectivity was not seen in reactions of other aldoses and ketoses. Recently, the above reaction has been conducted under two phase conditions 63b. A similar dimethylthetin anion 100 was used for the diastereocontrolled construction of glycidic acid (−)- 101 , which was further transformed into an important intermediate for the synthesis of 1α-hydroxylated vitamin D .…”
“…These results also aimed to correlate the absolute configuration of the major resulting trans -epoxyamides with the presence or absence of a protecting group of the C-2 hydroxyl. It was shown that the reaction of ylide 1 with compound 2 by the two-phase method produced only the stereoisomer 3 in a quantitative yield and with a configuration (2 R ,3 S ) opposite to that of the major product 5a (2 S ,3 R ) obtained in a lower yield from 4 . 1 …”
The reaction of N,N-diethyl-2-(dimethylsulfuranylidene)acetamide (1) with protected monosaccharides has been extended to several O-benzyl- and 4,6-O-Benzylidene-d-gluco- and -d-galactopyranose
derivatives. When the monosaccharide is 2,3,4,6-tetra-O-benzyl-d-glucose (6) or d-galactose (9),
elimination of the 3-benzyloxy substituent occurs, to give the unsaturated epoxyamides 7 and 10,
respectively, in reasonable yields and poor stereoselectivity. On the other hand, the reaction of 1
with the 4,6-O-benzylidene-d-glucopyranose derivatives 11, 14, and 17 yielded the corresponding
epoxyamides 12, 15a:15b, and 18a:18b in good yields and variable stereoselectivity. In accordance
with previous studies concerning the configurational assignments for the epoxide derivatives 3,
5a, and 21, obtained from 2, 4, and 20, respectively, the present article confirms the role of the
hydroxyl group at C-2 on the stereselectivity of the reaction. Thus, when the C-2 OH is unprotected
(4, 11, 20), the major epoxide formed has the configuration 2S, 3R (epoxyamides 5a, 12, and 21).
Conversely, derivatives with the hydroxyl group protected at C-2, or 2-deoxy sugars (2, 14, and
17), yield as the major epoxides the corresponding 2R, 3S isomers (3, 15b, and 18b).
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